This invention is generally directed to melt processable, intrinsically conductive and semiconductive polymeric composites useful in preparing electrically conductive films, coatings and articles with controlled conductivity. The conducting polymer composites of this invention can be manipulated in preparative processes to result in materials that are functional in many known applications for intrinsically conducting organic polymers, for example, molecular circuitry, electronic membranes, photovoltaics, light emitting diodes, electrochromic windows, rechargeable batteries, electrolytic capacitors, optical switches, and electromagnetic interference shielding. More specifically, the present invention is directed to conductive polymeric compositions containing therein, known conductive aromatic and heteroaromatic polymers, for example, poly(pyrrole), poly(thiophene) or poly(azulene) and their congeners in intimate admixture with an ionophoric or ionomeric block copolymer, that is, a block copolymer with an ion binding or ion coordinating segment and a nonfunctional segment to control morphology of the structured dispersed phase, and insure solubility and melt processability of the resulting polymeric composite conducting films and and functional articles. The ionophoric or ionomeric character of the block copolymer enables complexation or sequesteration of redox active dipolar molecules or ions in the binding segment of the block copolymer. The redox active ion or dipolar molecule, in embodiments of the present invention, acts as an oxidative coupling agent or redox reagent for the polymerization of heteroaromatic or aromatic monomers, yielding, Intrinsically Conductive organic Polymers (ICPs) which may be physically trapped or matrix polymerized to the ionophoric or ionomeric segment of the block copolymer.
The present invention thus provides soluble, melt processable, electronically conducting or semiconducting thermoplastic composites of intrinsically conducting organic polymers that are matrix polymerized to, or within, the ion-binding segments of ionophoric or ionomeric block copolymers. The present invention further specifies processes for the preparation of these composites and provides processes for making electrically conductive articles therefrom. The ICP composites may be prepared as colloidal solutions or in the solid state, with the material prepared in the solid state generally having higher conductivity.
The composite compositions of this invention are prepared in embodiments by template polymerization of aromatic and heteroaromatic monomers such as thiophene, pyrrole, indole, indene and azulene or a congener, for example, 3-methyl pyrrole, bithiophene, 3-alkylthiophenes, thianapththene, and the like, in the presence of an ionophoric or ionomeric block copolymer to which a suitable redox reagent for the oxidative coupling of the aromatic or heteraromatic monomer reactants, has been specifically bound.
Intrinsically conducting organic polymers, composites thereof, articles thereof, and processes for their preparation, are well known and are extensively documented in numerous prior art patents and publications, the disclosures of which are incorporated by reference herein in their entirety. Thus, for example, Rabek et al., Synthetic Metals, 45 (1991) 335-351, have described the polymerization of pyrrole in solid state FeCl3 complexes with poly(ethylene oxide), poly(oxy-1,2-ethane diyl), poly(xcex2-propiolactone), poly(2-oxetanone) or poly(1,5-di-oxepan-2-one). Jasne and Chicklis have described the electrochemical polymerization of pyrrole in latices with covalently bound anionic sites and Bates et al., J. Chem. Soc., Chem. Commun., (1985) 871, have described the preparation of a heat processable composite of poly(pyrrole) in sulfonated styrene (hydrogenated) butadiene triblock copolymer. Armes and Vincent, J. Chem. Soc., Chem. Commun., (1987) 288, described the preparation of colloidal poly(pyrrole) in water with agency of poly(vinyl pyrrolidone) or poly(vinyl alcohol-co-acetate). Poly(ethylene oxide), poly(acrylic acid) and block copolymers of poly(ethylene oxide) were specifically reported to be ineffective in stabilizing colloidal dispersions of poly(pyrrole). Similarly, Bjorklund Leidberg J. Chem. Soc., Chem. Commun., (1986) 1293, described the preparation of colloidal poly(pyrrole) in water with agency of methylcellulose. The seminal synthesis of poly(pyrrole) involved the electrochemical, oxidative coupling of pyrrole at electrode surfaces to directly yield conducting polymer films as reported by A. F. Diaz, K. K. Kanazawa and G. P. Gardini, J. Chem. Soc. Chem Comm., 635 (1979).
The chemical oxidative coupling polymerization of thiophene to yield conducting polymers is more difficult to effect, and accordingly poly(thiophene) is most often generated electrochemically. Garnier and coworkers reported the electropolymerization of thiophene, J. Electroanal. Chem., (1982) 135, 173, and the electropolymerization of thiophene in poly(methylmethacrylate) and poly(vinyl chloride), see J. Chem. Soc., Chem. Commun., (1986) 783; and J. Phys. Chem., 92 (1988), 833. The chemical synthesis of polythiophene with ferric perchlorate and ferric chloride/nitromethane was reported by M. Mermilliod-Thevenin and G. Bidan, Mol. Cryst. Liq. Cryst., 118:227 (1985), and S. Hotta, et al., Synthetic Metals, 9 (1984) 381. Koxcex2mehl (1986) Makromol. Chem., Macromol. Symp, 4:45 and (1982) Mol. Cryst. Liq. Cryst., 83:291, reported the chemical synthesis of poly(thiophene) with nitrosonium salts and Yamamoto et al., reported Grignard coupling to yield linear poly(thiophene), see (1981) Chem. Lett., 1079; and (1982) J. Polym. Sci., Polym. Lett. Ed., 20:365. Similarly, Elsebaumer, et al., reported Grignard coupling to yield poly (3-alkyl thiophenes). Alkylthiophene derivatives can be obtained as soluble polymer solutions, particularly when prepared by coupling of organolithium or organocadmium derivatives, Synthetic Metals, 18 (1987) 277.
Environmental instability, lack of mechanical strength and integrity, and difficulties in processing have represented major barriers to commercial application of intrinsically conducting organic polymers. Among ICPs, poly(pyrroles) and poly(thiophenes) are acknowledged to be among the most environmentally stable. Their synthesis is relatively simple. Recent work in leading enterprises seeking to exploit these polymers in the burgeoning commercial applications for intrinsically conducting polymers have focused on improved processing and the development of mechanical integrity in these materials. Poly(thiophenes), obtained by conventional processes are typically intractable, see for example, Advanced Materials, Volume 5, Number 9, September 1993, Part 2, page 646-650. Thus there remains a need for highly conducting, environmentally stable and easily processable polymer composite materials.
The preparative processes and procedures described in the literature fall into four main categories:
Category 1xe2x80x94The electrochemical polymerization of pyrrole or thiophene to directly yield the ICP in film form.
Category 2xe2x80x94The generation of colloidal ICP particles stabilized by selected water soluble polymers.
Category 3xe2x80x94The insitu generation of ICP within the interstices of a preformed polymer host into which a reagent for the oxidative polymerization has been imbibed. Subsequent exposure to the monomer yields a composite of the host polymer and the ICP. Alternatively, monomer (pyrrole or thiophene) may be imbibed into a preformed polymer film on an electrode surface and electrochemically polymerized within the interstices of a preformed polymer host.
Category 4xe2x80x94solublization of the ICP by polymerization of monomers with sufficiently long alkyl substituents. This approach has been particularly popular with poly(thiophene) where soluble polymers can be obtained from 3-alkylthiophene derivatives wherein the alkyl chain is C4 or longer. The processes of Categories 1 and 3 are generally limited to film geometries, and melt processing of the composition is not generally possible. The prior art processes for preparing ICPs, particularly those of Category 3, do not provide systems which possess the phase structured solutions, films and articles of the composite compositions of the present invention and therefore do not provide the manipulative and processing advantages associated therewith Colloidal ICP particles such as those generated by Category 2 processes are refractory powders and are not in themselves film forming. Accordingly, these materials must be physically dispersed in polymer hosts and thus offer no advantage over the widely used colloidal graphite composite compositions. With electrochemically polymerized films of pure ICP""s (Category 1) it is possible to vary the conductivity of the film by control of the oxidation state of the ICP. In ICP""s generated by the processes of category 3, it is not generally possible to vary the conductivity of the film by control of the oxidation state of the ICP rather conductivity is determined by approach to the percolation threshold in the composite.
Accordingly, there continues to be a need for improved electrically conducting or semiconducting polymeric materials, composites, films, and articles, and improved processes for preparing electrically conducting polymeric materials and articles thereof. Additionally, there continues to be a need for materials of precisely controlled conductivity or resistivity. Also, there continues to be a need for enhancements in thermal oxidative and hydrolytic stability of ICP""s. Additionally, there is a need for electrically conducting polymeric materials and composites which can be prepared by a simple, direct, and economical processes. Moreover, there is a need for ICP composites which can be extruded or injection molded. There is also a need for film forming ICP composites which may be conveniently solution cast from common hydrocarbon solvents.
The present invention in embodiments overcomes the performance and processability problems associated with the ICP compositions of the prior art by forming soluble colloidal composites comprised of a conducting aromatic or heteroaromatic polymer and an ionophoric or ionomeric block copolymer complex. The conductivity of the composite can be controlled by variation of the oxidation state of the ICP and/or by modulation of the structural morphology of the conductive polymeric composite particles. An important feature of the present invention is the specification of the precise set of polymeric composite compositions which are film forming, melt processable, and exhibit specific stable and controllable levels of conductivity.
It is an object of the present invention to provide polymeric composite compositions or intrinsically conducting organic polymer (ICP) compositions with controlled electrical conductivity.
It is a further object of the present invention to provide ICP composite compositions which are readily prepared and processed into films and useful articles.
It is another object of the present invention to provide ICP composite compositions which are processable by solvent-liquid means, that is by dissolving or forming micellar solutions, dispersions or suspensions in simple apolar or polar organic solvents.
It is another object of the present invention to provide ICP composite compositions which are environmentally stable.
It is another object of the present invention to provide ICP composite compositions which are processable by melt means such as extrusion, melt mixing, or molding.
It is an additional object of the present invention to provide ICP composite compositions possessing expanded or adjustable conductivity properties.
It is another object of the present invention to provide ICP composite compositions which exhibit the requisite mechanical properties for device and engineering plastics applications.
Additional objects and advantages of the invention will be apparent to those skilled in the art from the descriptions of compositions and processes for the preparation thereof which follows.
These and other objects of the present invention are accomplished in embodiments by providing a composite composition comprising: an aromatic or heteroaromatic polymer with regular or recurring units of pyrrole, indole, thiophene, thianaphthene, indene, azulene, and ring pendant substitutent derivatives thereof, such as alkyl, aryl, alkoxy, carboxyl, and cyano, nitro, or halogen substituents; and an ionophoric or ionomeric block or graft copolymer. These conductive and semiconductive composites may be formed in the solid state or in solution. The composites formed in structured solution are micellar or vesicular and resistive films may be cast from these colloidal solutions. Composites formed in the solid state are melt processable, are electrically conductive or semiconductive and are soluble in the sense that they may be dispersed in apolar solvents. The number of monomers in the aromatic or heteroaromatic conductive polymer is from about 10 to about 1010. The degree of polymerization in the aromatic or heteroaromatic conductive polymer varies from about 10 to about 1010 depending on the extent of cross linking or branching leading to highly networked polymers which may occur during oxidative coupling. Preferred aromatic or heteroaromatic pendant ring substituents include alkyl, aryl and alkoxy substituents because of their ready availability, solubility, stability, and ease of preparation. These substituents may, for example, contain from 1 to about 20 carbon atoms. The resulting compositions are typically soluble, melt processable, with electrical conductivity being highly controlled by the amount of heterocyclic polymer generated and the relative proportions of the apolar and ionophoric or ionomeric segments of the block or graft copolymer. Also contemplated in the present invention are processes for the preparation of the electrically conductive composite compositions and processes for preparing useful electrically conductive articles therefrom.
In embodiments of the present invention intrinsically conductive or semiconductive polymer (ICP) composites, and particularly, poly(thiophene) and poly(pyrrole), can be readily prepared with the agency of ion active block copolymers. By the term ion binding block copolymers is meant ionophoric and ionomeric block copolymers wherein there is at least one block segment of the copolymer that is capable of binding ionic species by either ionic or coordination bonding interactions and there is at least one block or segment of the copolymer that is incapable of or has a negligible affinity for ionic species. These ICP composites may be prepared as colloidal or structured solutions or in the solid state. It is generally the case that structured solution or solid state equilibrium morphologies in these block copolymer systems are more easily achieved prior to generation of the ICP in the ionophoric or ionomeric phase. The ICP composites prepared in the solid state generally possess greater conductivity than the ICP composites prepared in the structured or colloidal solutions. The relative conductivity of the compositions depends upon: 1.) the composition of the block copolymers, for example, higher conductivity being achieved in block copolymers with high volume factions, for example, greater than 30% by weight, of the ionophoric or ionomeric segment; 2.) the amount of ICP generated in the domain of the ionophoric or ionomeric segment; and 3.) the ability of the composite composition to reach an equilibrium morphology as a structured solution, or in the solid state.
The colloidal or structured solutions are appropriate for solution spraying, casting, or coating of articles or materials to yield structures coated with tough integral films of an intrinsically conductive or semiconductive composite. Alternatively, the colloidal solutions can be precipitated to yield thermoplastic powders which may be melt processed to yield conductive or semiconductive plastic articles or coatings.
The ICP composites, prepared directly in the solid state, are advantageous when highly conductive composites are required. In these systems, cylindrical, lamellar or bicontinuous morphologies, which may be achieved in embodiments, depending on the relative volume fractions of the ionomeric or ionophoric phase, are retained upon matrix polymerization of, for example, poly(thiophene) in the ion-binding phase. In these systems, the conductivity is controlled by the morphology and structure created by the block or graft copolymer and by the amount and oxidation state of the ICP generated within the ion binding phase. The nature of the oxidant (anion and cation) bound to the ion-binding segment of the block copolymer can also have a profound effect on the rate of polymerization, as well as the composite composition morphology and conductivity.
Ionophoric block copolymers which are suitable agents for the preparation of conductive or semiconductive composites of ICPs are typified by: poly(styrene-b-ethylene oxide), poly(butadiene-b-ethylene oxide), poly(styrene-b-ethyloxazoline), poly(styrene)-b-poly(oxime), poly(styrene)-b-poly(methylmethacrylate), and the like. With ionophoric block copolymers, the polymerization of the aromatic or heteraromatic monomer is accomplished by an oxidant or redox reagent which forms a specific complex with the ionophoric segment of the block copolymer. Salts of Fe3+, Cu2+, Sn4+, and Ce4+ ions, are particularly suitable oxidants as are peroxydisulfate, ferricyanide, I2/I3xe2x88x92, and peroxide salts of alkali and alkaline earth metals, such as sodium, potassium, magnesium, and calcium.
Ionomeric block copolymers which are suitable agents for the preparation of conductive or semiconductive composites of ICPs are, for example: poly(styrene-b-acrylic acid), poly(styrene-b-vinylsulfonic acid), and the like. Ionomeric block copolymers containing poly(carboxylic acid) segments are capable of coordinative or ion exchange binding of oxidative coupling reagents such as Fe3+, Cu2+, Sn4+, and Ce4+. Ionomeric block copolymers wherein the ionomeric segment is sulfonic acid or quaternary ammonium respectively, bind redox cations (Fe3+, Cu2+, Sn4+, and Ce4+) or anions, for example, peroxydisulfate or ferricyanide, preferably by ion exchange.
In both the ionophoric and ionomeric block copolymers, the apolar segment of the block copolymer provides solubility and processability and the ionomeric or ionophoric segment enables the formation of intrinsically conducting polymer within its interstices. The ionomeric or ionophoric phase may also provides a medium where a reservoir of counter ions essential to the facile redox cycling of intrinsically conductive polymers can be localized at distances from which they can rapidly diffuse into and out of the fractionally oxidized conducting polymer. This feature is particularly important to the enhanced performance characteristics for the compositions of this invention in electronic device applications.
The processes and compositions described herein and the products derived therefrom provide environmentally stable, intrinsically conducting polymer composites which can be processed in solution or in a xe2x80x9cmeltxe2x80x9d for a wide range of applications. The present invention also provides a means of varying the conductivity of the composite over a wide range, for example, 10xe2x88x9212 to 102 Siemens per cm. Deliberate variation of the relative volume fractions of the block copolymer segments by appropriate section of block copolymers and by controlling the amount of monomer and therefore the amount of heterocyclic homopolymer generated in the ionomeric or ionophoric phase provides a useful means for modulating the conductivity of the composition over the aforementioned conductivity range. Another useful means for controlling the apparent relative volume fraction of the ion binding B segment is to imbibe or add to the structured solution a homopolymer with a structure corresponding to the ion binding B segment in monomer composition of the block or graft copolymer in an amount from 25 to 150 percent by weight based on the weight of the ion binding B segment of the copolymer. Thus, for example in a structured solution formed from a PS-b-POE block copolymer, a POE homopolymer may be added before or after the addition of the redox salt.
Although not desired to be limited by theory, it is believed that the oxidative coupling of aromatic and heteroaromatic monomers leading to conductive homopolymers, such as poly(pyrrole) or poly(thiophene), is catalyzed by an oxidative coupling reagent bound to ionophoric or ionomeric segment in a diblock polymer to yield a heterocyclic our aromatic homopolymer phase which has been template polymerized within the ionophoric or ionomeric domain. In order to polymerize, the monomer must diffuse into the domains formed by the ionophoric or ionomeric segments where the redox reagent is bound. Once this is occurs, the aromatic or heteraromatic monomers are oxidized to generate radical cation species thereof which rapidly couple to yield linear or insoluble network polymers which are, at a minimum, physically entangled with the ionophoric or ionomeric segments. Even though the ICP product itself tends to be intractable, it is segregated within the ionophoric or ionomeric phase and therefore the solubility or dispersibility properties of the ICP composite is substantially improved. The thermoplastic nature of the apolar segment of the ion active diblock polymers imparts solubility and melt processability to the resulting composite compositions.
The level of conductivity is controlled primarily by the volume fraction of the ionophoric or ionomeric segment in the block copolymer. For block copolymers containing less than 25% by weight of the ionophoric or ionomeric component, the solid state morphology of the composite is typically that of an ordered close packed array of spherical domains (micelle cores) of the ionophoric or ionomeric polymer and the ICP. These systems will tend to be insulating with conductivities of about 10xe2x88x9210 Siemens per cm or less. For block copolymers containing greater than 25% and less than 35% by weight of the ionophoric or ionomeric component, the solid state morphology of the composite is likely to exhibit vesicular, cylindrical or worm like structures. For polymeric composite systems containing greater than 35% by weight of the ion binding component lamellar and bicontinuous morphologies can be achieved and the conductivity of these compositions approaches those conductivities exhibited by pure ICP""s, of about 10xe2x88x923 to 102 Siemens per cm.